Higher: amino acids and polypeptides

Two different functional groups

An amino acid contains an amino group, –NH₂, and a carboxylic-acid group, –COOH. Glycine, H₂NCH₂COOH, is a simple example. Having two different reactive groups in one molecule allows amino-acid molecules to join in a chain. The nitrogen belongs to the amino group; it should not be mistaken for the n written outside polymer brackets to represent many repeats.